Lubricating system for power unit for vehicle with internal combustion engine

ABSTRACT

A lubricating system for a power unit for a vehicle with an internal combustion engine. A static oil hydraulic type non-stage transmission is disposed on a left lateral side of a crankshaft, and a lubricating oil tank is formed integrally with a main body of the internal combustion engine and is disposed on a right lateral side opposite to the side of the transmission, with the crankshaft therebetween.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lubricating system in a power unitfor a vehicle with an internal combustion engine by which the power ofan internal combustion engine having a crankshaft directed in thefront-rear direction of the vehicle is transmitted to wheels through astatic oil hydraulic type non-stage transmission.

2. Description of the Related Art

There has been known a lubricating system for a power unit for a vehiclewith an internal combustion engine in which a static oil hydraulic typenon-stage transmission comprised of a swash plate type oil hydraulicpump and a swash plate type oil hydraulic motor is incorporatedintegrally with an internal combustion engine, wherein a lubricating oiltank is integrally mounted to the front surface of a case of the powerunit. The lubricating oil flowing down to a bottom portion of the spaceinside the power unit is sucked up by a recovery pump, and is chargedinto the lubricating oil tank. The lubricating oil in the lubricatingoil tank is supplied to the portions to be lubricated of the internalcombustion engine and to the static oil hydraulic type non-stagetransmission by a supply pump. An example of such a lubricating systemis disclosed in Japanese Patent Laid-open No. 2001-343060.

In the above-mentioned lubricating system for the power unit for avehicle with an internal combustion engine, the lubricating oil tank isseparate from the power unit and is integrally mounted to the outsidesurface of the power unit. Therefore, the number of component parts isincreased, which also increases costs.

In addition, since the static oil hydraulic type non-stage transmissionis relatively large in weight and is disposed on either one of the leftand right sides of the crankshaft of the internal combustion engine, inorder to establish the proper balance between the left side and theright side of the vehicle body it has been necessary to take intoaccount the conditions of arrangement of various shafts in the powerunit and the conditions of arrangement of various component parts.

The present invention pertains to a lubricating system for a power unitfor vehicle with internal combustion engine, and has been made forsolving the problems in the above-mentioned prior art.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a lubricating system for a powerunit for a vehicle with an internal combustion engine is provided. Thesystem includes an internal combustion engine having a crankshaftdirected in the front-rear direction of a vehicle body, a static oilhydraulic non-stage transmission having a swash plate oil hydraulic pumpand a swash plate oil hydraulic motor, and a lubricating oil tank for alubricating oil to be supplied to individual portions of the internalcombustion engine and to the transmission. The transmission is disposedon either one of the left and right sides of the crankshaft, and thelubricating oil tank is formed integrally with a main body of the powerunit for vehicle or a main body of the internal combustion engine and isdisposed on a lateral side opposite to the side of the static oilhydraulic type non-stage transmission, with the crankshaft therebetween.

In another aspect of the present invention, a power unit for a vehiclewith an internal combustion engine is provided. The system comprises aninternal combustion engine having a crankshaft directed in a front-reardirection of a vehicle body; a static oil hydraulic non-stagetransmission comprised of a swash plate oil hydraulic pump and a swashplate oil hydraulic motor; and tank means for holding a lubricating oilto be supplied to individual portions of the internal combustion engineand to the transmission. The transmission is disposed on either the leftor right side of the crankshaft, and the tank means is formed integrallywith a main body of the power unit and is disposed on a lateral side ofthe crankshaft that is opposite to the side on which the transmission isdisposed.

Thus, the static oil hydraulic type non-stage transmission is disposedon either one of the left and right sides of the crankshaft directed inthe front-rear direction of the vehicle, and the lubricating oil tank isdisposed on the other of the left and right sides of the crankshaft.Therefore, even if the static oil hydraulic type non-stage transmissionis comparatively large in weight, the weight balance between the leftside and the right side of the power unit for vehicle with internalcombustion engine can be easily taken by utilizing the weight of thelubricating oil tank and the weight of the lubricating oil charged inthe lubricating oil tank.

Moreover, since the lubricating oil tank is formed integrally with themain body of the power unit for vehicle or the main body of the internalcombustion engine, the lubricating oil tank is firmly connected to themain body, and the number of component parts is largely reduced, wherebyreductions in cost and weight and an enlargement of the tank capacitycan be realized.

In another aspect of the present invention, the lubricating tank is notonly constituted by the crankcase for bearing the crankshaft but alsoconstituted by the crankcase cover making contact with an outsidesurface of the crankcase and covering the outside surface of thecrankcase, so that a further enlargement of the capacity of thelubricating oil tank can be achieved.

Moreover, since the crankcase and the crankcase cover can both be easilydie-cast or cast, a further enhancement of productivity and a furtherreduction in cost can be achieved.

In yet another aspect of the present invention, a recovery pump by whicha lubricating oil dropping to a bottom portion of the inside of thecrankcase is returned to the lubricating oil tank and a supply pump forsupplying the lubricating oil from the lubricating oil tank toindividual portions of the internal combustion engine and to the staticoil hydraulic type non-stage transmission are disposed coaxially.Therefore, the overall size of a lubricating oil pump comprised of bothof the pumps is reduced, whereby the lubricating oil pump can be reducedin weight and size, and an oil passage between the lubricating oil pumpsand an oil passage between the lubricating oil pump and the lubricatingoil tank are shortened, thereby decreasing pump losses.

In another aspect of the present invention, an oil filter for filteringthe lubricating oil to be supplied from the lubricating oil tank toindividual portions of the internal combustion engine and to the staticoil hydraulic type non-stage transmission is disposed at a position onthe front side of the lubricating oil tank and overlapping with thelubricating oil tank as viewed forwards with respect to the vehicle, sothat the lubricating oil tank and the oil filter are close to eachother. Therefore, the oil relieved from the filter is immediately fedback into the lubricating oil tank, and, since the oil filter is closeto the lubricating oil pump, pump losses can be is reduced.

Moreover, since the oil filter is located on the front side of the powerunit, maintenance, inspection and repair of the oil filter can becarried out simply and easily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a vehicle on which a power unit according tothe present invention is mounted.

FIG. 2 is a front view, as viewed from the front side, of the power unitshown in FIG. 1.

FIG. 3 is a cross-sectional view of the power unit for vehicle withinternal combustion engine, taken along line III—III of FIG. 1.

FIG. 4 is a vertical sectional view of the power unit for vehicle withinternal combustion engine shown in FIG. 1.

FIG. 5 is a vertical sectional view of a static oil hydraulic typenon-stage transmission of the present invention.

FIG. 6 is a front view of a front case cover of the present invention.

FIG. 7 is a front view of a front crankcase of the present invention.

FIG. 8 is a rear view of the front crankcase of the present invention.

FIG. 9 is a front view of a rear crankcase of the present invention.

FIG. 10 is a rear view of the rear crankcase of the present invention.

FIG. 11 is a front view of a rear case cover of the present invention.

FIG. 12 is a rear view of the rear case cover of the present invention.

FIG. 13 is a plan view of the front crankcase and the rear crankcase ofthe present invention.

FIG. 14 is a sectional view taken along line XIV—XIV of FIG. 6.

FIG. 15 is a sectional view taken along line XV—XV of FIG. 6.

FIG. 16 is a sectional view taken along line XVI—XVI of FIG. 6.

FIG. 17 is a sectional view taken along line XVII—XVII of FIG. 6.

FIG. 18 is a sectional view taken along line XVIII—XVIII of FIG. 6.

FIG. 19 is a sectional view taken along line XIX—XIX of FIG. 6.

FIG. 20 is a sectional view taken along line XX—XX of FIG. 7.

FIG. 21 is a sectional view taken along line XXI—XXI of FIG. 7.

FIG. 22 is an enlarged view of a part of FIG. 9.

FIG. 23 is a sectional view taken along line XXIII—XXIII of FIG. 10.

FIG. 24 is a sectional view taken along line XXIV—XXIV of FIG. 12.

FIG. 25 is a sectional view taken along line XXV—XXV of FIG. 22.

FIG. 26 is a plan view, as viewed from above, of the shape of the bottomsurface of a cylinder block of the present invention.

FIG. 27 is a sectional view taken along line XXVII—XXVII of FIG. 26.

FIG. 28 is a sectional view taken along line XXVIII—XXVIII of FIG. 27.

FIG. 29 is a top view of the cylinder block of the present invention.

FIG. 30 is a plan view, as viewed from above, of the shape of the bottomsurface of a cylinder head of the present invention.

FIG. 31 is a top view of the cylinder head of the present invention.

FIG. 32 is a front view of a lubricating oil pump of the presentinvention.

FIG. 33 is a sectional view taken along line XXXIII—XXXIII of FIG. 32.

FIG. 34 is an illustration of the outline of a lubricating oil circuitaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Now, an embodiment of a power unit for a vehicle with an internalcombustion engine 1 according to the present invention shown in thedrawings will be described. In this embodiment, the upward and downwarddirections mean the upward and downward directions with respect to thevehicle body, the front side means the front side with respect to thevehicle body, the rear side means the rear side with respect to thevehicle body, and the left and right mean the left and right as viewedfrom a person directed toward the front side.

Overall Structure

As shown in FIG. 1, in an off-road four-wheel vehicle 0 on which thepower unit for vehicle with internal combustion engine 1 is mounted,pairs of front wheels 3 and rear wheels 4 are disposed respectively atfront and rear portions of a vehicle body frame 2, the front end rearends of transmission shafts directed in the forward and rearwarddirections from the power unit for vehicle with internal combustionengine 1 are connected to the front wheel 3 and the rear wheel 4 throughdifferential devices (not shown) and a front axle 6 and a rear axle 7,respectively, and the four-wheel vehicle 0 can run in a four-wheel drivemode by the power from the power unit 1.

In addition, the four-wheel vehicle 0 includes a bar handle 8 at acentral portion in the width direction on the front side, a steeringmechanism 10 is provided at the lower end of a steering shaft 9connected to the bar handle 8, and a swiveling operation on the barhandle 8 is transmitted to the front wheels 3 through the steering shaft9 and the steering mechanism 10, whereby the four-wheel vehicle 0 can beturned to the left or the right.

Further, a fuel tank 11 is mounted on the vehicle body frame 2 whilebeing located on the upper side of the power unit 1, a seat 12 ismounted on the rear side thereof, a fan 13 and an oil cooler 14 aresequentially disposed on the front side of the power unit 1, acarburetor 15 and an air cleaner 16 are sequentially disposed on therear side of the power unit for vehicle with internal combustion engine1, and the front axle 6 and the rear axle 7 are supported on the vehiclebody frame 2 through shock absorbers 17.

Furthermore, as shown in FIGS. 2, 3 and 4, the power unit 1 includes a4-stroke-cycle internal combustion engine 20, a static oil hydraulictype non-stage transmission 100, and a speed change drive shaftcontroller 150. The 4-stroke-cycle internal combustion engine 20 is anoverhead-valve push-rod type single-cylinder internal combustion enginehaving a cylinder center axis in the vertical direction with respect tothe front-rear direction, as shown in FIG. 1, and slightly inclined fromthe vertical direction to the left, as viewed forwards from the rearside of the vehicle body, with respect to the left-right direction, asshown in FIG. 3. As shown in FIGS. 4 and 5, the static oil hydraulictype non-stage transmission 100 is a transmission in which a swash platetype oil hydraulic pump 110 and a swash plate type oil hydraulic motor130 are disposed on the same axis in the front-rear direction and whichchanges the speed of rotation from a crankshaft 28 of the 4-stroke-cycleinternal combustion engine 20. The speed change drive shaft controller150 includes a speed change drive shaft 151 for reciprocating a drivemember 152 for changing the swash plate angle of the swash plate typeoil hydraulic pump of the swash plate type oil hydraulic motor 130.

In addition, in the 4-stroke-cycle internal combustion engine 20, asshown in FIGS. 1 and 4, a crankcase is partitioned into four portions,namely, into a front case cover 21, a front crankcase 22, a rearcrankcase 23 and a rear case cover 24 in the front-rear direction, withvertical planes directed in the vehicle width direction as fayingsurfaces, a cylinder block 25, a cylinder head 26 and a head cover 27are sequentially stacked on the upper side of the front crankcase 22 andthe rear crankcase 23 at the center in the front-rear direction, and thefront case cover 21, the front crankcase 22, the rear crankcase 23, therear case cover 24, the cylinder block 25, the cylinder head 26 and thehead cover 27 are mutually integrally connected by bolts and the likewhich are not shown.

Further, as shown in FIG. 3 (the many-dotted portion in the figure meansa faying surface between one member and another), the crankshaft 28 isrotatably borne on the front crankcase 22 and the rear crankcase 23while being directed in the front-rear direction (see FIG. 4), and apiston 30 is slidably fitted in a cylinder bore 29 in the cylinder block25 directed roughly in the vertical direction. The upper and lower endsof a connecting rod 31 are rotatably fitted on a piston pin 30 ainserted in the piston 30 and a crank pin 28 a on the crankshaft 28, andthe crank shaft 28 is driven to rotate by the pressure of a combustiongas generated by the combustion of a mixture gas that is sucked into acombustion chamber 32 surrounded by the cylinder bore 29, the cylinderhead 26 and the piston 30.

Furthermore, the cylinder head 26 is provided with an intake port 33opened rearwards and an exhaust port 34 opened forwards, and is providedwith an intake valve 35 and an exhaust valve 36 for openably closing theports of the intake port 33 and the exhaust port 34 on the side of thecombustion chamber 32, respectively. The carburetor 15 and the aircleaner 16 (see FIG. 1) are connected to a rear opening portion of theintake port 33, whereas an exhaust gas clarifier, a muffler and thelike, which are not shown, are connected to a front opening portion ofthe exhaust port 34 through an exhaust pipe 18. As shown in FIG. 3, aspark plug 39 is screwed to the cylinder head 26 so that an electrodeportion 39 a of the spark plug 39 faces the combustion chamber 32.

The cylinder block 25 and the cylinder head 26 are provided with coolingfins 37 and cooling fins 38, respectively. A running airflow arisingfrom the running of the vehicle and a cooling airflow generated by a fan13 come into contact with the cooling fins 37 and 38, whereby the4-stroke-cycle internal combustion engine 20 is cooled. Also, as will bedescribed later, the 4-stroke-cycle internal combustion engine 20 iscooled by a cooling lubricating oil that passes inside the cylinderblock 25 and the cylinder head 26.

In addition, as shown in FIG. 3, in the cylinder block 25 and thecylinder head 26, a communication hole 40 is formed on the right side ofthe cylinder bore 29 and substantially in parallel to the cylinder bore29, and a circular guide hole 41 is formed in top walls of the frontcrankcase 22 and the rear crankcase 23 at a position directly below thecommunication hole 40. At a position on the downward extension of thecommunication hole 40 and the guide hole 41, a camshaft 43 is rotatablyborne on camshaft pivot holes 67 c and 71 c provided in partition walls67 and 71 of the front crankcase 22 and the rear crankcase 23. A valvelifter 45 slidably fitted in the guide hole 41 is brought into contactwith a cam 44 on the camshaft 43. A front-rear pair of rocker arms 46are oscillatably borne on the cylinder head 26, with rocker shafts 42shown in FIG. 4 therebetween, in parallel to contact surfaces betweenthe cylinder block 25, the cylinder head 26 and the head cover 27. Apush rod 47 is interposed between one end portion of the rocker arm 46and the valve lifter 45, and the other end portion of the rocker arm 46is brought into contact with the top end of the intake valve 35 or theexhaust valve 36. In each of the intake valve 35 and the exhaust valve36, a valve spring 49 is interposed between a valve spring retainer 48mounted on the top end and a spring receiving portion 26 a of thecylinder head 26. A chain which is not shown is set around a drivesprocket 50 (see FIG. 4) fitted on the crankshaft 28 and a drivensprocket (not shown) fitted on the camshaft 43 and having a number ofteeth of two times that of the drive sprocket 50. When the crankshaft 28is rotated, the camshaft 43 is driven to rotate in a ratio of onerevolution to two revolutions of the crankshaft 28, and the intake valve35 and the exhaust valve 36 are opened and closed one time eachcorresponding to two revolutions of the crankshaft 28, with the samevalve timing as that in an ordinary 4-stroke-cycle internal combustionengine.

As shown in FIG. 4, at a rear portion of the crankshaft 28, a balancerdrive gear 51 is integrally mounted to the crankshaft 28 at a positionon the rear side of the drive sprocket 50. As shown in FIG. 3, abalancer gear 52 meshed with the balancer drive gear 51 is borne on thefront crankcase 22 and the rear crankcase 23 through a balancer shaft 53at a position on the right side of the crankshaft 28. Further, an ACG 54(AC generator) is disposed on the rear side of the balancer drive gear51, a rotor 54 a of the ACG 54 is fitted in the vicinity of a rear endportion of the crankshaft 28, a recoil starter 55 is provided at a rearend portion of the crankshaft 28 on the rear side of the rotor 54 a, apump drive gear 56 is integrally mounted to a front portion of thecrankshaft 28, and a starting clutch 57 is provided at the front end ofthe crankshaft 28 at a position on the front side of the pump drive gear56.

Further, as shown in FIG. 4, a drive gear 58 is integrally attached to aclutch outer 57 a, which is an output member of the starting clutch 57.As shown in FIGS. 3 and 4, the static oil hydraulic type non-stagetransmission 100, located slightly on the upper side and on the leftside of the crankshaft 28, is disposed inside the front crankcase 22 andthe rear crankcase 23. As shown in FIG. 5, an oil hydraulic motor rotaryshaft 131 of the swash plate type oil hydraulic motor 130 in the staticoil hydraulic type non-stage transmission 100 is rotatably borne on thefront case cover 21 and the rear crankcase 23. A motor casing 132 of theswash plate type oil hydraulic motor 130 is rotatably borne on the oilhydraulic motor rotary shaft 131. A driven gear 101 is integrallyattached to a pump casing 111 of the swash plate type oil hydraulic pump110 rotatably borne on the oil hydraulic motor rotary shaft 131. Asshown in FIG. 4, the driven gear 101 is meshed with the drive gear 58 ofthe starting clutch 57. When the drive gear 58 of the starting clutch 57is rotated, the pump casing 111 of the swash plate type oil hydraulicpump 110 in the static oil hydraulic type non-stage transmission 100 isdriven to rotate, with the oil hydraulic motor rotary shaft 131 as acenter.

In addition, as shown in FIG. 4, a gear transmission 160 is disposed inthe space surrounded by the rear crankcase 23 and the rear case cover24, and a main shaft 161 of the gear transmission 160 is spline-fittedto the oil hydraulic motor rotary shaft 131 of the static oil hydraulictype non-stage transmission 100. As shown in FIG. 3, a counter shaft 162is disposed at a position on the left lower side of the main shaft 161,and, further, an output shaft 163 is disposed at a position on the rightlower side of the counter shaft 162 and the main shaft 161. The mainshaft 161, the counter shaft 162 and the output shaft 163 are rotatablyborne on the rear crankcase 23 and the rear case cover 24. A countergear 166, normally in mesh with a main gear 165 integral with the mainshaft 161, is rotatably mounted on the counter shaft 162, and a shifter167 is mounted on the counter shaft 162 so that it cannot rotate but canaxially slide in relation to the counter shaft 162. A counter outputgear 168 integral with the counter shaft 162 and a gear 169 integralwith the output shaft 163 mesh with each other. When the shifter 167slides forwards by a change-over mechanism (not shown) so as to engagewith the counter gear 166, the counter gear 166 and the counter shaft162 are connected to each other, whereby the rotating force of the mainshaft 161 is transmitted to the output shaft 163.

Moreover, as shown in FIG. 4, a reverse counter gear 170, locatedbetween the shifter 167 and the counter output gear 168, is rotatablymounted to the counter shaft 162. As shown in FIG. 3, a reverse shaft164 located adjacent to the main shaft 161 and the counter shaft 162 isrotatably borne on the rear crankcase 23 and the rear case cover 24 (seeFIG. 4), an input gear 171 on one side which is integral with thereverse shaft 164 is meshed with the main gear 165 on the main shaft161, and an output gear 172 on the other side which is integral with thereverse shaft 164 is meshed with the reverse counter gear 170 on thecounter shaft 162. When the shifter 167 slides rearwards, the counteroutput gear 168 and the counter shaft 162 are connected to each other,whereby the rotating force of the main shaft 161 is transmitted, in areverse rotating condition, to the output shaft 163 through the reverseshaft 164 and the counter shaft 162.

Both the front and rear ends of the output shaft 163 are connectedrespectively to the transmission shafts 5 disposed on the front and rearsides of the power unit 1, so that the rotating force of the outputshaft 163 is transmitted to the front wheels 3 and the rear wheels 4through the transmission shafts 5 and through the front axle 6 and therear axle 7.

In addition, as shown in FIG. 3, the speed change drive shaft controller150 is disposed on the upper left side of the power unit 1, and theangle α between a plane connecting the center line of the speed changedrive gear 151 of the speed change drive shaft controller 150 and thecenter line of the oil hydraulic motor rotary shaft 131 of the staticoil hydraulic type non-stage transmission 100 and the center line of thecylinder bore 29 of the 4-stroke-cycle internal combustion engine 20 isas extremely small as about 10°.

Further, as shown in FIGS. 3 and 4, the speed change drive shaft 151 ofthe speed change drive shaft controller 150 is provided with a malescrew at a central portion in the longitudinal direction thereof, andthe drive member 152 is meshed with the speed change drive shaft 151 ofthe male screw. As shown in FIG. 5, the drive member 152 is oscillatablyconnected to arm portions 134, which project in a forked form from amotor swash plate 133 of the swash plate type oil hydraulic motor 130 inthe static oil hydraulic type non-stage transmission 100, through a pin135. As shown in FIG. 5, a gear 153 integral with the speed change driveshaft 151 is meshed with a small gear 155 of a speed reduction gear 154,and a large gear 156 of the speed reduction gear 154 is meshed with apinion gear 159 integral with a rotary shaft 158 of a control motor 157.By the normal and reverse rotations of the control motor 157, the drivemember is driven forwards and rearwards, whereby the inclination angleof the motor casing 132 of the swash plate type oil hydraulic motor 130is controlled.

Furthermore, as shown in FIG. 3, along a plane orthogonal to the planeconnecting the speed change drive shaft 151 of the speed change driveshaft controller 150 and the oil hydraulic motor rotary shaft 131 of theswash plate type oil hydraulic motor 130, a speed change ratio sensor102 is disposed at a position on the left side of the swash plate typeoil hydraulic motor 30.

Lubricating Oil Pump

Next, a lubricating oil pump 60 will be described.

As shown in FIGS. 6 and 7, which are views as viewed rearwards from thefront side of the front case cover 21 and the front crankcase 22, and inFIG. 4, which is a sectional view taken along a vertical plane in thefront-rear direction, the lubricating oil pump 60 is integrally attachedto the front case cover 21 and the front crankcase 22 so that the frontand rear surfaces of the lubricating oil pump 60 make close contact withthe rear surface of the front case cover 21 and the front surface of thefront crankcase 22, respectively. As shown in the enlarged views ofFIGS. 32 and 33, the lubricating oil pump 60 includes of a trochoid typerecovery pump 61 and a supply pump 62 which are arranged on the samepump rotary shaft 63. The recovery pump 61 and the supply pump 62include inner rotors 61 a, 62 a mounted to the pump rotary shaft 63,outer rotors 61 b, 62 b meshed with the inner rotors 61 a, 62 a, andpump bodies 61 c, 62 c rotatably enclosing the outer rotors 61 b, 62 b,respectively. The outer rotors 61 b, 62 b are eccentric relative to theinner rotors 61 a, 62 a, and the numbers of teeth of the outer rotors 61b, 62 b are greater than the numbers of teeth of the inner rotors 61 a,62 a by one.

As shown in FIG. 4, a pump gear 63 a integrally attached to the pumprotary shaft 63 of the lubricating oil pump 60 is meshed with a pumpdrive gear 56 integral with the crankshaft 28. Attendant on the rotationof the crankshaft 28, the pump rotary shaft 63 is driven to rotate,whereby in the recovery pump 61 the lubricating oil is sucked in througha suction port 61 d and discharged through a discharge port 61 e, and inthe supply pump 62 the lubricating oil is sucked in through a suctionport 62 d and discharged through a discharge port 62 e.

Crankcase

The specific structures of the front case cover 21, the front crankcase22, the rear crankcase 23 and the rear case cover 24 constituting thecrankcase of the 4-stroke-cycle internal combustion engine 20 will bedescribed.

As shown in FIGS. 4 and 6, the front case cover 21 is providedintegrally with a filter case 65 of the oil filter 64, and a filterelement 66 (see FIG. 4) is contained in the filter case 65. Thelubricating oil flowing into the filter case 65 through an inflowpassage 65 a at an outer circumferential portion of the filter case 65is filtered by the filter element 66, and is then discharged into acentral oil passage 65 b.

In addition, as shown in FIGS. 7 and 8, the front crankcase 22 isprovided integrally with a partition wall 67 parallel to the front andrear faying surfaces of the front crankcase 22, substantially at thecenter in the front-rear and width directions. The partition wall 67 isprovided with the following. A crankshaft hole 67 a for passing thecrankcase 28 therethrough. A transmission loose-fitting hole 67 b forloose fitting therein of the static oil hydraulic type non-stagetransmission 100 at a position on the left side in the crankcase. Acamshaft hole 67 c for passing and supporting the camshaft 43 therein. Abalancer shaft hole 67 d for passing and supporting the balancer shaft53 threin at a position on the lower side of the camshaft hole 67 c. Aspeed change drive shaft hole 67 e for passing the speed change driveshaft 151 of the speed change drive shaft controller 150 therethroughand an output shaft hole 67 f for passing and supporting the outputshaft 163 therein, at positions on the upper and lower sides of thetransmission loose fitting hole 67 b. A crank chamber communication hole67 g and a recovery pump suction communication hole 67 h incommunication with the suction port 61 d of the recovery pump 61, whichare located on the lower side of the counter shaft hole 67 f. A supplypump suction communication hole 67 i in communication with the suctionport 62 d of the supply pump 62, and a strainer lower lubricating oilsump 67 j ranging leftwards from the position directly below therecovery pump suction communication hole 67 h.

Further, as shown in FIG. 7, in the front crankcase 22, a tank partitionwall 68 projected forwards beyond the partition wall 67 is provided at arequired spacing along a right side wall 22 a (on the left side in FIG.7) of the front crankcase 22. As shown in FIG. 8, a tank partition wall69 projected rearwards beyond the partition wall 67 is provided at aposition different from that of the tank partition wall 68 butsubstantially along the tank partition wall 68. A crank chamber 59 andan oil tank chamber 70 are partitioned by the tank partition wall 68 andthe tank partition wall 69, and the partition wall 67 is provided withtank communication holes 67 k (at four locations) at positions on theright outer side of the tank partition wall 68 and the tank partitionwall 69 (the partition wall 67 is provided with only these holes).

Furthermore, as shown in FIG. 8, the tank partition wall 69 projectedrearwards beyond the partition wall 67 is provided with a cutout 69 b inan extension portion 69 a extended to the right upper side at a slant(left upper side at a slant in FIG. 8) of the portion partitioning thecrank chamber 59 and the oil tank chamber 70 so that the lubricating oildwelling on the upper surface of the tank partition wall 69 flowsdownwards through the cutout 69 b to be led to the strainer lowerlubricating oil sump 67 j.

The front crankcase 22 is provided with mount holes 22 b in both lowerside portions thereof. Rod-like members (not shown) penetrating throughthe mount holes 22 b and mount holes 23 b formed in both lower sideportions of the rear crankcase 23 are integrally mounted to the vehiclebody frame 2 through rubber bushes (not shown).

In addition, as shown in FIGS. 9 and 10, like the front crankcase 22,the rear crankcase 23 is integrally provided with a partition wall 71parallel to the front and rear faying surfaces of the rear crankcase 23,at the center in the front-rear and width directions thereof. Thepartition wall 71 is provided with the following. A crankshaft hole 71 afor passing the crankshaft 28 therethrough. An oil hydraulic motorrotary shaft hole 71 b for rotatably bearing the oil hydraulic motorrotary shaft 131 of the swash plate type oil hydraulic motor 130 in thestatic oil hydraulic type non-stage transmission 100. A camshaft hole 71c for passing and supporting the camshaft 43 therein. A balancer shafthole 71 d for passing and supporting the balancer shaft 53 therein at aposition on the lower side of the camshaft hole 71 c. A counter shafthole 71 e for passing and supporting the counter shaft 162 therein at aposition intermediate between the main shaft 161 and the output shaft163 and on the left side. An output shaft hole 71 f for passing andsupporting the output shaft 163 therein at a position on the lower sideof the oil hydraulic motor rotary shaft hole 71 b. A crank chambercommunication hole 71 g at a position on the slanted right lower side ofthe output shaft hole 71 f. A reverse shaft hole 71 m (shown in FIG. 10only) for supporting the reverse shaft 164 at a position intermediatebetween the main shaft 161 and the output shaft 163 and on the rightside.

As shown in FIG. 9, the rear crankcase 23 is provided with a strainerlower lubricating oil sump 71 j in communication with the strainer lowerlubricating oil sump 67 j of the crankcase 22, and is provided with acommunication portion 71 h in communication with the recovery pumpsuction communication hole 67 h at a position on the upper side of thestrainer lower lubricating oil sump 71 j. A strainer 85 is fitted inboth side cutouts 71 l between the strainer lower lubricating oil sump71 j and the communication portion 71 h.

Further, as shown in FIG. 9, the rear crankcase 23 is provided with atank partition wall 72 (the tip end surface of the tank partition wall72 can make contact with the rear end surface of the tank partition wall69 of the front crankcase 22) projected forwards beyond the partitionwall 71 at a required spacing along a right side wall 23 a (on the leftside in FIG. 9) of the rear crankcase 23, and, as shown in FIG. 10, therear crankcase 23 is provided with a tank partition wall 73 projectedrearwards beyond the partition wall 71 at a position different from thetank partition wall 72 but substantially along the tank partition wall72 so that the crank chamber 59 and the oil tank chamber 70 arepartitioned by the tank partition wall 72 and 73. The partition wall 71is provided with tank communication holes 71 k (at six locations) atpositions on the right outer side of the tank partition wall 72 and thetank partition wall 73. As shown in FIG. 10, an upper end portion 73 aof the tank partition wall 73 and a top wall portion 23 c of the rearcrankcase 23 are not connected to each other but are separated from eachother, so that a gap 73 b is formed between the upper end portion 73 aof the tank partition wall 73 and the top wall portion 23 c of the rearcrankcase 23.

As shown in FIG. 9, the tank partition wall 72 projected forwards beyondthe partition wall 71 is provided with a cutout 72 b in its extensionportion 72 a curvedly extended to the right upper side at a slant sothat the lubricating oil dwelling on the upper surface of the tankpartition wall 72 flows downwards through the cutout 72 b to be led tothe strainer lower lubricating oil sump 71 j.

Furthermore, as shown in FIG. 10, at a rear portion of the rearcrankcase 23, an overflow oil passage wall 74 projected rearwards fromthe rear surface of the partition wall 71 is extended downwards from thetop wall portion 23 c of the rear crankcase 23 so that a requiredspacing is present at a position on the upper left side of the tankpartition wall 73. The lower front end 74 a of the overflow oil passagewall 74 is extended to the crank chamber communication hole 71 g of thepartition wall 71, and an overflow oil passage 75 is constituted of thetank partition wall 73 and the overflow oil passage wall 74.

As shown in FIGS. 3 and 5, a breather chamber 80 is disposed on thecenter axis of the speed change drive shaft 151 of the speed changedrive shaft controller 150. As shown in FIGS. 5, 9, 23 and 25, thepartition wall 71 is not present at a left upper portion (a right upperportion in FIG. 9) of the rear crankcase 23 corresponding to thebreather chamber 80, and a breather chamber bottom wall 76 flush withthe rear faying surface of the rear crankcase 23 is provided there. Abreather partition portion 77 for partitioning the breather chamber 80is projected forwards from the breather chamber bottom wall 76, and thebreather partition portion 77 is provided with a cutout portion 77 a asshown in FIG. 25.

In addition, a shaft support portion 76 a projected forwards from asubstantially central portion of the breather chamber bottom wall 76 isprovided with a threaded hole 76 b. An outer circumferential edgeportion 78 b of a top wall 78 a of a breather cover 78, L-shaped insection as shown in FIG. 5, is brought into contact with an innercircumferential step portion 23 e of a left top wall 23 d of the rearcrankcase 23, as shown in FIG. 23. A bolt 79 penetrating through a holeformed at a central recessed portion 78 c of the top wall 78 a of thebreather cover 78 is screwed into the threaded hole 76 b in the shaftsupport portion 76 a so that the breather chamber 80 is constituted ofthe left top wall 23 d of the rear crankcase 23, the breather chamberbottom wall 76, the breather partition portion 77 and a bent wall 78 dof the breather cover 78.

Further, the breather chamber bottom wall 76 is provided with an opening76 b. As shown in FIG. 5, one end of a breather pipe 81 is fitted in theopening 76 b, and the other end of the breather pipe 81 is connected toan intake system of the 4-stroke-cycle internal combustion engine 20through a pipe, a hose and the like which are not shown.

Furthermore, a tank partition wall 82 and an overflow oil passage wall83 (shown in FIG. 11) whose tip end surfaces can make contact with therear end surfaces of the tank partition wall 73 and the overflow oilpassage wall 74 projected rearwards beyond the partition wall 71 of therear crankcase 23 (shown in FIG. 10) are projected forwards at the frontsurface of the rear case cover 24, as shown in FIG. 11.

The rear case cover 24 is provided with an opening 24 a in which the ACG54 can be fitted, and, as shown in FIG. 12, a contact portion 24 b withwhich the casing 54 b of the ACG 54 can make contact is formed at anouter circumferential rear surface of the opening 24 a.

Cylinder Block, Cylinder Head

FIG. 13 is a plan view in which the rear surface of the front crankcase22 and the front surface of the rear crankcase 23 are laid on eachother. Under the condition where an opening 25 p of the communicationhole 40 in the cylinder block 25 shown in FIG. 26 coincides withopenings 22 p and 23 p formed in the front crankcase 22 and the rearcrankcase 23. A cylinder bottom portion faying surface 25 x of thecylinder block 25 is laid on cylinder block faying surfaces 22 x and 23x of the front crankcase 22 and the rear crankcase 23. Cylinder sleeveinsertion holes 22 r and 23 r are composed of semi-circular cutouts inthe top walls of the front crankcase 22 and the rear crankcase 23, and acylinder sleeve 25 r (see FIG. 4) of the cylinder block 25 is fitted inthe cylinder sleeve insertion holes 22 r and 23 r.

In addition, FIG. 29 is a top view of the cylinder block 25. Under thecondition where an opening 26 p of the communication hole 40 in thecylinder head 26 shown in FIG. 30 coincides with the opening 25 p of thecommunication hole 40 in the cylinder block 25, a cylinder head bottomportion faying surface 26 y of the cylinder head 26 is laid on acylinder head faying surface 25 y of the cylinder block 25, and lowerend screws of four bolts (not shown) penetrating through bolt holes 26 aand 25 a formed in the cylinder head 26 and the cylinder block 25 arescrewed into bolt holes 22 q and 23 q respectively formed in the frontcrank case 22 and the rear crankcase 23, whereby the cylinder block 25,the cylinder head 26, the front crankcase 22 and the rear crankcase 23are mutually integrally connected.

Further, as shown in FIG. 3, the outer circumferential surface of thehead cover 27 is brought into contact with the top surface of thecylinder head 26, and the head cover 27 is integrally connected to thecylinder head 26 by bolts or the like, which are not shown.

Lubricating Oil Circuit

Referring to FIG. 34, in this embodiment, the outline of a lubricatingoil circuit through which the lubricating oil in the 4-stroke-cycleinternal combustion engine 20 is supplied to individual portions of thepower unit 1 will be described. The suction port 61 d of the recoverypump 61 is connected to the crank chamber 59 through the strainer 85,the discharge port 61 e of the recovery pump 61 is connected to asuction port 14 a of the oil cooler 14, and a discharge port 14 b of theoil cooler 14 is connected to the ACG 54, the cylinder block 25 and thecylinder head 26 and is connected to the oil tank chamber 70.

The suction port 62 d of the supply pump 62 is connected to a bottomportion of the oil tank chamber 70, the discharge port 62 e of thesupply pump 62 is connected to the suction port 65 a of the oil filter64, and the discharge port 65 b of the oil filter 64 is connected to thestatic oil hydraulic type non-stage transmission 100, the 4-stroke-cycleinternal combustion engine 20 and the starting clutch 57.

Further, the discharge ports 61 e and 62 e of the recovery pump 61 andthe supply pump 62 are connected to the crank chamber 59 and the oiltank chamber 70 through relief valves 86 and 87, respectively.

Next, the crank chamber 59 and the oil tank chamber 70, integrallyconstituted inside the front case cover 21, the front crankcase 22, therear crankcase 23 and the rear case cover 24, are partitioned by thepartition wall 67 of the front crankcase 22 into front and rearportions. In the front portion, the crank chamber 59 and the oil tankchamber 70 are partitioned into left and right portions by the tankpartition wall 68 of the front crankcase 22 (shown in FIG. 7) and a tankpartition wall 89 formed of the front case cover 21 correspondingly tothe tank partition wall 68. In a central portion in the front-reardirection intermediately bound between the partition wall 67 of thefront crankcase 22 and the partition wall 71 of the rear crankcase 23,the crank chamber 59 and the oil tank chamber 70 are partitioned intoleft and right portions by the tank partition wall 69 of the frontcrankcase 22 (shown in FIG. 8) and the tank partition wall 72 of therear crankcase 23 (shown in FIG. 9). The crank chamber 59 and the oiltank chamber 70 are partitioned by the partition wall 71 of the rearcrankcase 23 into front and rear portions. At the rear portion, thecrank chamber 59 and the oil tank chamber 70 are partitioned into leftand right portions by the tank partition wall 73 (shown in FIG. 10) andthe tank partition wall 82 (shown in FIG. 11).

In addition, as shown in FIGS. 7 and 8, the crank chamber 59 at thefront portion and the crank chamber 59 at the central portion in thefront-rear direction are mutually communicated through the crank chambercommunication hole 67 g formed in the partition wall 67 of the frontcrankcase 22 and the strainer lower lubricating oil sump 67 j. As shownin FIGS. 9 and 10, the crank chamber 59 at the central portion in thefront-rear direction and the crank chamber 59 at the rear portion aremutually communicated through the crank chamber communication hole 71 gformed in the partition wall 71 of the rear crankcase 23 and thestrainer lower lubricating oil sump 71 j.

Further, as shown in FIGS. 7 and 8, the oil tank chamber 70 at the frontportion and the oil tank chamber 70 at the central portion in thefront-rear direction are mutually communicated through the tankcommunication holes 67 k (at four locations) formed in the partitionwall 67 of the front crankcase 22. As shown in FIGS. 9 and 10, the oiltank chamber 70 at the central portion in the front-rear direction andthe oil tank chamber 70 at the rear portion are mutually communicatedthrough the tank communication holes 71 k (at six locations) formed inthe partition wall 71 of the rear crankcase 23.

Oil passages formed inside the front case cover 21, the front crankcase22, the rear crankcase 23, the rear case cover 24, the cylinder block 25and the cylinder head 26 will be described specifically, according tothe lubricating oil circuit shown in FIG. 34.

As shown in FIGS. 6 and 7, the suction port 61 d of the recovery pump 61is connected to the recovery pump suction communication hole 67 h of thefront crankcase 22. When the rotary shaft 63 of the lubricating oil pump60 is driven to rotate, the lubricating oil dwelling in the strainerlower lubricating oil sumps 67 j and 71 j is filtered through thestrainer 85 as shown in FIG. 9, and then flows through the communicationportion 71 h of the rear crankcase 23 and the recovery pump suctioncommunication hole 67 h of the front crankcase 22 into the suction port61 d of the recovery pump 61.

In addition, as shown in FIGS. 6 and 14, the discharge port 61 e of therecovery pump 61 is connected to an opening 21 a on the rear side of thefront case cover 21, the opening portion 21 a is in communication with afront end opening 21 c through a communication passage 21 b directedforwards, and the opening 21 c and the inflow port 14 a of the oilcooler 14 are connected to each other through a hose, a pipe and thelike, which are not shown, so that the lubricating oil discharged fromthe discharge port 61 e of the recovery pump 61 is fed to the oil cooler14. As shown in FIG. 14, the branch passage 21 d is branched from thecommunication passage 21 b, and a relief valve 86 is interposed in thebranch passage 21 d. When the lubricating oil pressure in thecommunication passage 21 b reaches or exceeds a predetermined setpointpressure, the relief valve 86 operates so that the lubricating oil isreturned from the branch passage 21 d into the crank chamber 59 throughan opening 21 e.

Further, the discharge port 14 b of the oil cooler 14 is connected to areturn port 21 f of the front case cover 21 shown in FIG. 6 through ahose, a pipe and the like, which are not shown. As shown in FIG. 15, thereturn port 21 f is in communication with an opening 21 h through acommunication passage 21 g, and to the oil tank chamber 70 through anorifice 21 i.

Furthermore, as shown in FIGS. 6 and 7, the opening 21 h of the frontcase cover 21 and an opening 22 h of the front crankcase 22 coincidewith each other, and, as shown in FIG. 20, the opening 22 h is incommunication with an opening 22 j through a communication passage 22 i.

As shown in FIG. 13, the opening 22 j opened in the cylinder blockfaying surface 22 x of the front crankcase 22 coincides with an opening25 j opened in the cylinder bottom portion faying surface 25 x of thecylinder block 25 shown in FIG. 26. As shown in FIG. 27, the opening 25j is in communication with an opening 25 l in the cylinder head fayingsurface 25 y of the cylinder block 25 through a vertical communicationpassage 25 k. As shown in FIGS. 29 and 30, the opening 25 l in thecylinder block 25 coincides with a communication passage 26 l in thecylinder head 26, and the upper end of the communication passage 26 l isexposed into the space surrounded by the head cover 27.

As shown in FIGS. 26 and 27, the vertical communication passage 25 k anda vertical communication passage 25 n parallel thereto are mutuallycommunicated through a communication passage 25 m extending in thefront-rear direction, the upper end opening 25 o of the verticalcommunication passage 25 n coincides with an opening 26 o in thecylinder head 26, and the upper end of the opening 26 o is also exposedto the spacing surrounded by the head cover 27.

Further, the lower end opening 25 s of the vertical communicationpassage 25 n in the cylinder block 25 shown in FIG. 27 is incommunication with an opening 23 s in the rear crankcase 23 shown inFIG. 13. As shown in FIG. 22, the opening 23 s is in communication withan opening 23 u through a communication passage 23 t, and the opening 23u in the rear crankcase 23 is in communication with an opening 24 u inthe rear case cover 24 shown in FIG. 11. As shown in FIG. 24, theopening 24 u is in communication with an opening 24 w through acommunication passage 24 v, and the opening 24 w in the rear case cover24 is in communication with an ACG lubricating oil jet port (not shown)provided in a cover 54 b (see FIG. 4) of the ACG 54.

As has been described above, the lubricating oil fed to the oil cooler14 by the recovery pump 61 and cooled by the oil cooler 14 is fed to thereturn port 21 f in the front case cover 21 shown in FIG. 15, passedthrough the communication passage 21 g, is jet into the oil tank chamber70 through the orifice 21 i, and is allowed to dwell in the oil tankchamber 70. The lubricating oil dwelling in the oil tank chamber 70 issucked into the suction port 62 d of the supply pump 62 through thesupply pump suction communication hole 67 i opened into the oil tankchamber 70, and the pressure lubricating oil pressurized by the supplypump 62 is fed through the discharge port 62 e of the supply pump 62 toa discharge port 21 j in the front case cover 21, as shown in FIG. 16.

The discharge port 21 j in the front case cover 21 shown in FIG. 16 isconnected to the inflow passage 65 a in the filter case 65 of the oilfilter 64. As shown in FIGS. 4 and 19, the discharge passage 65 b in thefilter case 65 is connected to a center hole 131 a in the oil hydraulicmotor rotary shaft 131 of the static oil hydraulic type non-stagetransmission 100, and is connected to a center hole 68 b in thecrankshaft 28 through an orifice 65 c shown in FIGS. 4 and 19. As shownin FIG. 4, the center hole 68 b is in communication with a clutchcommunication hole 68 c. Thus, the cooled lubricating oil filtered bythe oil filter 64 is supplied to the static oil hydraulic type non-stagetransmission 100 and the crankshaft 28.

In addition, as shown in FIG. 17, in the front case cover 21, a reliefvalve 87 is interposed in a communication passage 65 d between thecommunication between a filter chamber in the filter case 65 and thecrank chamber 59 (the left side in the figure). As shown in FIG. 18, abranch passage 65 e is branched from a discharge passage 65 b in thefilter case 65, a check valve 88 is interposed in the branch passage 65e, and a lubricating oil jet port 65 f is formed from the branch passage65 e toward the starting clutch 57 in the crank chamber 59. When thepressure inside the filter chamber in the filter case 65 exceeds apredetermined value, the lubricating oil is ejected into the crankchamber 59 through the relief valve 87. In addition, when thelubricating oil pressure inside the discharge passage 65 b in the filtercase 65 exceeds a predetermined value, the lubricating oil is ejectedinto the crank chamber 59 through the check valve 88. Further, thelubricating oil in the discharge passage 65 b in the filter case 65 isjetted through the lubricating oil jet port 65 f toward the startingclutch 57.

Since the embodiment shown in the drawings is constituted as describedabove, when the 4-stroke-cycle internal combustion engine 20 is startedby operating the recoil starter 55 in the condition where the countergear 166 and the counter shaft 162 are connected to each other by movingthe shifter 167 forwards, the 4-stroke-cycle internal combustion engine20 is put into an operating condition. When the rotational frequency ofthe crankshaft 28 exceeds a predetermined rotational frequency, thestarting clutch 57 is put into a connected condition, and the pumpcasing 111 of the static oil hydraulic type non-stage transmission 100is driven to rotate.

The oil hydraulic motor rotary shaft 131 is driven to rotate at arequired speed change ratio according to the magnitude of theinclination angle of the motor swash plate 133 of the swash plate typeoil hydraulic motor 130 set correspondingly to the axial position of thedrive member 152 in the speed change drive shaft controller 150, thespeed of the counter shaft 162 is reduced at a predetermined speedchange ratio at the gear transmission 160, and the power is transmittedfrom the output shaft 163 to the front wheels 3 and the rear wheels 4through the front and rear transmission shafts 5 and through the frontaxle 6 and the rear axle 7, whereby the four-wheel vehicle 0 can bemoved forwards.

In addition, as shown in FIG. 3, the angle a between the planeconnecting the swash plate type oil hydraulic pump 110 of the static oilhydraulic type non-stage transmission 100, the oil hydraulic motorrotary shaft 131 on the center line of the swash plate type oilhydraulic motor 130 and the speed change drive shaft 151 of the speedchange drive shaft controller 150 and the center line of the cylinderbore 29 is as small as about 10°. Besides, on the left side of the4-stroke-cycle internal combustion engine 20, the static oil hydraulictype non-stage transmission 100 and the speed change drive shaftcontroller 150 are disposed close to the 4-stroke-cycle internalcombustion engine 20. Therefore, the size in the width direction of thepower unit for vehicle with internal combustion engine 1 is small,providing a compact design, which improves the mountability of the powerunit on the four-wheel vehicle 0.

Further, since the speed change ratio sensor 102 is disposed on the leftouter side of the static oil hydraulic type non-stage transmission 100,the maintenance, inspection and repair of the speed change ratio sensor102 can be easily carried out from the left side of the four-wheelvehicle 0.

Furthermore, the breather chamber 80 is located on the left upper sideof the crank chamber 59 and disposed on the extension line of the speedchange drive shaft 151 of the speed change drive shaft controller 150,and the static oil hydraulic type non-stage transmission 100 is disposedon the lower side thereof. Therefore, the lubricating oil dropletsscattered from the crankshaft 28 and the main gear 165, counter gear166, shifter 167, counter output gear 168 and gear 169 of the geartransmission 160 are shielded by the static oil hydraulic type non-stagetransmission 100, thereby being inhibited from reaching the left upperside of the crank chamber 59, and a blow-by gas with a low oil mistmixing ratio is introduced into the breather chamber 80. As a result,the breather chamber 80 may be small in capacity, and can be simplifiedin structure.

Moreover, since the crankshaft 28 is directed in the front-reardirection of the vehicle body, the ACG 54, the recoil starter 55, thestarting clutch 57 and the gear transmission 160 are arranged in thefront-rear direction of the vehicle body, which, in cooperation with thearrangement of the static oil hydraulic type non-stage transmission 100and the speed change drive shaft controller 150 close to the center axisof the cylinder bore 29, promises a further reduction of the size of thepower unit 1 and a further enhancement of the mountability thereof onthe four-wheel vehicle 0.

In addition, as shown in FIG. 3, the static oil hydraulic type non-stagetransmission 100 is disposed on the left side in the space inside thecrankcase composed of the front case cover 21, the front crankcase 22,the rear crankcase 23 and the rear case cover 24, and the oil tankchamber 70 is disposed on the right side in the space inside thecrankcase. Therefore, it is easy to take the weight balance between theleft and right sides of the power unit 1 by utilizing the weight of thestatic oil hydraulic type non-stage transmission 100 and the weight ofthe lubricating oil in the oil tank chamber 70.

Further, as shown in FIG. 6, the tank partition wall 89 is integrallyprojected from the inside wall surface of the front case cover 21. Asshown in FIGS. 7 and 8, the tank partition wall 68 and the tankpartition wall 69 are integrally projected forwards and rearwards fromthe partition wall 67 of the front crankcase 22. As shown in FIGS. 9 and10, the tank partition wall 72 and the tank partition wall 73 areintegrally projected forwards and rearwards from the partition wall 71of the rear crankcase 23. As shown in FIG. 11, the tank partition wall82 is integrally projected rearwards from the inside wall surface of therear case cover 24. Therefore, there is no need for special componentparts for constituting the oil tank chamber 70, the weight and thenumber of working steps are reduced, and the crankcase can be reduced inweight and cost and enhanced in rigidity.

Furthermore, the oil tank chamber 70 is formed between the frontcrankcase 22 and the rear crankcase 23 by the tank partition wall 69(see FIG. 8) projected rearwards from the partition wall 67 of the frontcrankcase 22 and the tank partition wall 72 (see FIG. 9) projectedforwards from the partition wall 71 of the rear crankcase 23. The oiltank chamber 70 is formed between the front case cover 21 and the frontcrankcase 22 by the tank partition wall 89 (see FIG. 6) projectedrearwards from the inside wall surface of the front case cover 21 andthe tank partition wall 68 (see FIG. 7) projected forwards from thepartition wall 67 of the front crankcase 22. The oil tank chamber 70 isformed between the rear crankcase 23 and the rear case cover 24 by thetank partition wall 73 (see FIG. 10) projected rearwards from thepartition wall 71 of the rear crankcase 23 and the tank partition wall82 (see FIG. 11) projected forwards from the inside wall surface of therear case cover 24. Therefore, the capacity of the oil tank chamber 70is extremely large.

Moreover, since the front case cover 21, the front crankcase 22, therear crankcase 23 and the rear cover case 24 can be die-cast or cast, afurther enhancement of productivity and a further reduction in cost canbe achieved.

In addition, the recovery pump 61 by which the lubricating oil dwellingin the strainer lower lubricating oil sumps 67 j and 71 j at bottomportions inside the crankcase is fed to the oil tank chamber 70 and thesupply pump 62 by which the lubricating oil is supplied from the oiltank chamber 70 to the crankshaft 28 and the starting clutch 57 of the4-stroke-cycle internal combustion engine 20 and the static oilhydraulic non-stage transmission 100 are arranged coaxially. Therefore,the overall size of the lubricating oil pump 60 composed of the recoverypump 61 and the supply pump 62 is reduced, and the lubricating oil pump60 can be reduced in size and weight. Further, the oil passage betweenthe recovery pump 61 and the supply pump 62 and the oil passage betweenthe lubricating oil pump 60 and the oil tank chamber 70 are shortened,whereby the pump loss of the lubricating oil pump 60 is reduced.

Further, the filter case 65 of the oil filter 64 for filtering thelubricating oil to be supplied from the oil tank chamber 70 to theindividual portions of the 4-stroke-cycle internal combustion engine 20and the static oil hydraulic type non-stage transmission 100 is arrangedat a position on the front side of the oil tank chamber 70 andoverlapping with the oil tank chamber 70 as viewed in the front-reardirection of the vehicle body. Therefore, the oil tank chamber 70 andthe oil filter 64 are arranged close to each other, and the lubricatingoil in the oil filter 64 is immediately returned into the oil tankchamber 70 through the relief valve 87 interposed in the communicationpassage 65 d of the oil filter 64, so that the pump loss of the supplypump 62 is low.

Furthermore, the oil filter 64 is located on the front side of the frontcase cover 21; therefore, as shown in FIG. 4, a cover 64 a of the oilfilter 64 can be easily removed on the front side of the four-wheelvehicle 0, replacement of the filter element 66 can be easily carriedout, and the maintenance, inspection and repair of the oil filter 64 canbe carried out quickly and easily.

In addition, as for the cylinder block 25, the cylinder head 26 and theACG 54, which do not need a filtered lubricating oil but need a cooledlubricating oil, the lubricating oil cooled by passing through the oilcooler 14 is supplied directly to the cylinder block 25, the cylinderhead 26 and the ACG 54 without passing through the oil filter 64.Therefore, the load on the supply pump 62 can be reduced, the power losswith respect to the supply pump 62 can be greatly reduced, and thesupply pump 62 can be reduced in size.

As shown in FIG. 15, the lubricating oil fed to the oil cooler 14 by therecovery pump 61 and cooled by the oil cooler 14 flows through thereturn port 21 f of the front case cover 21 and the communicationpassage 21 g to reach the opening 21 h, and is fed from the opening 22 hof the front crankcase 22 shown in FIG. 20 to the opening 22 j throughthe communication passage 22 i. As shown in FIGS. 13, 26 and 27, thelubricating oil is fed from the opening 22 j of the front crankcase 22to the top surface opening 25 l of the cylinder block 25 through thebottom surface opening 25 j and the vertical communication passage 25 kin the cylinder block 25. Further, as shown in FIGS. 29, 30 and 31, thelubricating oil reaches the top opening 26 l of the cylinder head 26,flows out through the top surface opening 26 l to the top surface of thecylinder head 26, and drops from the cylinder head 26 back into thecrank chamber 59 through the communication hole 40, whereby the cylinderblock 25 and the cylinder head 26 are cooled.

In addition, as shown in FIG. 27, the communication passage 25 m isbranched from the vertical communication passage 25 k. Therefore, a partof the lubricating oil rising through the vertical communication passage25 k flows through the communication passage 25 m to reach the verticalcommunication passage 25 n, and the lubricating oil flowing in an upperportion of the vertical communication passage 25 n flows out through thetop surface opening 26 o to the top surface of the cylinder head 26 inthe same manner as the lubricating oil flowing through the top surfaceopening 26 l, and drops through the communication hole 40 into the crankchamber 59, whereby the cylinder block 25 and the cylinder head 26 arecooled.

Further, the lubricating oil flowing in a lower portion of the verticalcommunication passage 25 n flows through the bottom surface opening 25 sof the cylinder block 25 to reach the opening 23 s in the rear crankcase23, is fed through the communication passage 23 t shown in FIG. 22 tothe opening 23 u, is fed from the opening 23 u through the opening 24 uand the communication passage 24 v in the rear case cover 24 shown inFIG. 24 to the opening 24 w, and is jetted through the lubricating oiljet port of the ACG 54, whereby the ACG 54 is cooled.

Further, the cooled lubricating oil sucked up from the crank chamber 59to be supplied to the oil cooler 14 by the recovery pump 61 and cooledby the oil cooler 14 is not supplied to the oil filter 64 but supplieddirectly to the cylinder block 25 and the cylinder head 26. Therefore,the cylinder block 25 and the cylinder head 26 are not only cooled bythe air cooling, in which a cooling airflow blasted rearwards by the fan13 and a running airflow caused by running the vehicle are brought intocontact with the cooling fins 37 and the cooling fins 38, but alsocooled by the lubricating oil cooling in which the cooled lubricatingoil passes inside the cylinder block 25 and the cylinder head 26. As aresult, the cylinder block 25 and the cylinder head 26, and hence theportion surrounding the combustion chamber 32, are cooled sufficiently.

Furthermore, the lubricating oil cooled by the oil cooler 14 is alsosupplied to the recoil starter 54 without passing through the oil tankchamber 70, so that the recoil starter 54 is also cooled sufficiently.

In addition, upper end edges 73 a and 82 a of the tank partition wall 73projected rearwards from the partition wall 71 (shown in FIG. 10) andthe tank partition wall 82 projected forwards from the inside wallsurface (shown in FIG. 11) are located on the lower side of upper endedges 89 a and 68 a of the tank partition wall 89 projected rearwardsfrom the inside wall surface of the front cover case 21 (shown in FIG.6) and the tank partition wall 68 projected forwards from the partitionwall 67 of the front crankcase 22 (shown in FIG. 7). Further, thepartition wall 67 of the front crankcase 22 is provided with the tankcommunication hole 67 k, and the partition wall 71 of the rear crankcase23 is provided with the tank communication hole 71 k. Therefore, the oilsurfaces of the lubricating oil in the oil tank 70 are all maintained atthe same level, and the lubricating oil in the oil tank chamber 70 cancalmly flow into the overflow oil passage 75 and the overflow oilpassage 84 via the upper end edges 73 a and 82 a of the tank partitionwall 73 and the tank partition wall 82 which are low in height. As aresult, the lubricating oil in the crank chamber 59 is prevented frombeing stirred by the crankshaft 28, whereby power loss and generation ofmist of the lubricating oil are reduced. Also, the lubricating oil isled into the strainer lower lubricating oil sumps 67 j and 71 j at thebottom portions of the crank chamber 59 smoothly and calmly, whereby thegeneration of bubbles is also reduced.

Further, as shown in FIGS. 10 and 11, the overflow oil passages 75 and84 are constituted of the tank partition wall 73, the tank partitionwall 82 and overflow oil passage walls 74 and 83, which are formedintegrally with the rear crankcase 23 and the rear case cover 24,respectively. Therefore, the overflow oil passages 75 and 84 areextremely simplified in structure, which reduces manufacturing costs.

Furthermore, the oil tank chamber 70 between the rear crankcase 23 andthe rear case cover 24 is formed in a crescent shape along the rightside wall 23 a of the rear crankcase 23 (the right side wall of the rearcase cover 24 is not denoted by any symbol). Therefore, the tankpartition wall 73, the tank partition wall 82 and the overflow oilpassage walls 74 and 83 are also formed in similar shapes, so that thelubricating oil having flowed over partition wall upper edges 73 a and82 a of the oil tank chamber 70 is led to the strainer lower lubricatingoil sumps 67 j and 71 j at the bottom portions of the crank chamber 59,without generating a turbulent flow.

The present invention should not be considered limited to the particularexamples or materials described above, but rather should be understoodto cover all aspect of the invention as fairly set out in the attachedclaims. Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

1. A power unit for a vehicle with an internal combustion enginecomprising: an internal combustion engine having a crankshaft directedin a front-rear direction of a vehicle body; a static oil hydraulicnon-stage transmission comprised of a swash plate oil hydraulic pump anda swash plate oil hydraulic motor; and a lubricating oil tank forholding a lubricating oil to be supplied to individual portions of theinternal combustion engine and to the transmission, wherein thetransmission is disposed on either the left or right side of thecrankshaft, and the lubricating oil tank is formed integrally with amain body of the power unit and is disposed on a lateral side of thecrankshaft that is opposite to the side on which the transmission isdisposed.
 2. The power unit for a vehicle with an internal combustionengine as set forth in claim 1, wherein the lubricating tank is formedintegrally with a main body of the internal combustion engine.
 3. Thepower unit for a vehicle with an internal combustion engine as set forthin claim 1, wherein the lubricating oil tank is formed over the range ofa crankcase for bearing the crankshaft and a crankcase cover makingcontact with an outside surface of the crankcase and covering theoutside surface of the crankcase.
 4. The power unit for a vehicle withan internal combustion engine as set forth in claim 1, wherein an oilpump is disposed substantially directly below the crankshaft, and theoil pump comprises: a recovery pump by which a lubricating oil droppedto a bottom portion of the inside of the crankcase is returned to thelubricating oil tank; and a supply pump for supplying the lubricatingoil from the lubricating oil tank to individual portions of the internalcombustion engine and to the transmission through an oil filter, therecovery pump and the supply pump being disposed coaxially.
 5. The powerunit for a vehicle with an internal combustion engine as set forth inclaim 4, wherein the oil filter is disposed at a position on a frontside of the lubricating oil tank and overlapping with the lubricatingoil tank as viewed forwards with respect to the vehicle.
 6. The powerunit for a vehicle with an internal combustion engine as set forth inclaim 2, wherein an oil pump is disposed substantially directly belowthe crankshaft, and the oil pump comprises: a recovery pump by which alubricating oil dropped to a bottom portion of the inside of thecrankcase is returned to the lubricating oil tank; and a supply pump forsupplying the lubricating oil from the lubricating oil tank toindividual portions of the internal combustion engine and to thetransmission through an oil filter, the recovery pump and the supplypump being disposed coaxially.
 7. The power unit for a vehicle with aninternal combustion engine as set forth in claim 6, wherein the oilfilter is disposed at a position on the front side of the lubricatingoil tank and overlapping with the lubricating oil tank as viewedforwards with respect to the vehicle.
 8. A power unit for a vehicle withan internal combustion engine comprising: an internal combustion enginehaving a crankshaft directed in a front-rear direction of a vehiclebody; a static oil hydraulic non-stage transmission comprised of a swashplate oil hydraulic pump and a swash plate oil hydraulic motor; and tankmeans for holding a lubricating oil to be supplied to individualportions of the internal combustion engine and to the transmission,wherein the transmission is disposed on either the left or right side ofthe crankshaft, and the tank means is formed integrally with a main bodyof the power unit and is disposed on a lateral side of the crankshaftthat is opposite to the side on which the transmission is disposed. 9.The power unit for a vehicle with an internal combustion engine as setforth in claim 1, wherein the tank means is formed integrally with amain body of the internal combustion engine.
 10. The power unit for avehicle with an internal combustion engine as set forth in claim 1,wherein the tank means is formed over the range of a crankcase forbearing the crankshaft and a crankcase cover making contact with anoutside surface of the crankcase and covering the outside surface of thecrankcase.
 11. The power unit for a vehicle with an internal combustionengine as set forth in claim 8, wherein an oil pump is disposedsubstantially directly below the crankshaft, and the oil pump comprises:recovery means for recovering lubricating oil dropped to a bottomportion of the inside of the crankcase and returning it to the tankmeans; and supply means for supplying the lubricating oil from the tankmeans to individual portions of the internal combustion engine and tothe transmission through an oil filter.
 12. The power unit for a vehiclewith an internal combustion engine as set forth in claim 11, wherein theoil filter is disposed at a position on a front side of the lubricatingoil tank and overlapping with the lubricating oil tank as viewedforwards with respect to the vehicle.
 13. The power unit for a vehiclewith an internal combustion engine as set forth in claim 10, wherein anoil pump is disposed substantially directly below the crankshaft, andthe oil pump comprises: recovery means for recovering lubricating oildropped to a bottom portion of the inside of the crankcase and returningit to the tank means; and supply means for supplying the lubricating oilfrom the lubricating oil tank to individual portions of the internalcombustion engine and to the transmission through an oil filter.
 14. Thepower unit for a vehicle with an internal combustion engine as set forthin claim 13, wherein the oil filter is disposed at a position on thefront side of the lubricating oil tank and overlapping with thelubricating oil tank as viewed forwards with respect to the vehicle.